Gas chromatography (GC) was introduced in 1951 and is now the most widely used instrumental chemical analysis technique. By use of GC, various components of a volatile sample stream may be separated. The technique includes the recovery and/or detection of one or more specific chromatographic fractions from a gas effluent stream exiting from the chromatographic column. The gas effluent stream typically comprises a carrier gas and a series of separated fractions of the sample in the gas phase. These fractions are eluted or withdrawn from the column outlet in a particular order and over a particular time interval.
At present, isothermal gas chromatography (ITGC) and programmed temperature gas chromatography (PTGC) are commonly practiced. The instrumentation required to implement these two modes of operation is widely available. In both of these techniques, a separation column is centrally placed within a thermally controlled chamber, specifically a GC oven. In ITGC operation, the column temperature is maintained constant. In contrast, in PTGC operation, the whole column temperature is increased as a function of time from a low initial value to some elevated setting. In both of these two modes of gas chromatography, temperature is constant along the column axis.
Although there are no commercially available chromatographs capable of imparting a negative-temperature gradient along the column axis, these types of gradients have been provided in chromathermographic methods. Basically, chromathermography component separation is achieved by moving a temperature field along the length of the chromatographic column. Both stationary and non-stationary methods have been practiced. I define non-stationary chromathermography as one method in which a moving oven is used. This moving oven contains a linear temperature gradient along the oven axis so that the temperature at the beginning of the oven is higher than at its opposite end. The oven is moved axially along the column length so that the direction of the moving temperature field coincides with the carrier flow.
I define stationary chromathermography to mean that there is no moving oven in the method. A fluid, most often a liquid, is used to deliver the desired temperature gradient with the gradient being a negative value. In addition to a fluid, electrical heaters can be used to achieve the same objective. Most often, the temperature gradient is linear in nature.
Although a myriad of analyses are conducted annually using GC, many areas of technological improvement are still needed. For instance, there is a need in the art for the provision of an apparatus and method that reduce analysis times and can provide effective separation of heretofore difficult-to-separate samples. Additionally, there is a need for a device and method suited to analyze even trace-levels of particular sample components.